Recently, the use of ozone has attracted much attention in the semiconductor fabrication industry. Ozone has been found to be effective in cleaning a surface of a semiconductor wafer by oxidizing undesirable organic and/or metallic materials, such as photoresist residue, which can then be removed from the wafer surface. Depending on the cleaning process, a layer of oxide may be formed on the cleaned surface of the semiconductor wafer as a result of the cleaning process. Such a layer of oxide is commonly referred to as a native oxide layer. In addition to cleaning, ozone has been found to be similarly effective in simply growing a layer of oxide on a desired surface of a semiconductor wafer. The grown oxide layers, including native oxide layers, may be used as passivation or interfacial layers for semiconductor devices.
Ozone can be applied to a surface of a semiconductor wafer using a dry or wet technique. Dry ozone application techniques involve exposing a surface of a semiconductor wafer to ozone gas, alone or with one or more gases, to oxidize the materials on the wafer surface. Wet ozone application techniques involve exposing a surface of a semiconductor wafer to both ozone and a processing fluid, such as deionized (DI) water or a chemical solution. Such wet ozone application techniques have been found to be highly effective in promoting oxidization. One wet ozone application technique involves dispensing a processing fluid onto a surface of the semiconductor wafer, which is in a closed processing chamber, and introducing ozone gas into the closed processing chamber. The dispensed processing fluid on the surface of the semiconductor wafer forms a layer of processing fluid on the wafer surface. When the ozone gas is introduced into the closed processing chamber, the ozone gas reaches the surface of the semiconductor wafer by diffusing through the processing fluid layer to oxidize materials on the wafer surface. Another wet ozone application technique involves immersing a semiconductor wafer in a bath of processing fluid with dissolved ozone gas. Thus, the surface of the semiconductor wafer is exposed to both the ozone and the processing fluid. Still another technique involves dispensing a processing fluid with dissolved ozone gas onto a surface of a semiconductor wafer to expose the wafer surface to both the ozone and the processing fluid.
A concern with the above-described wet ozone application techniques is that the rate of oxidation is relatively low due to a number of factors. One factor is that the concentration of ozone in a typical processing fluid is very low. For example, the concentration of ozone in DI water is roughly 2–40 ppm at room temperature. Another factor is that ozone decays in processing fluids, such as DI water and NH4OH solution. The ozone decay rate depends on the temperature of the processing fluid and the chemicals included in the processing fluid. Consequently, the use of heated processing fluid and/or processing fluid having certain chemicals may not be practical, although such processing fluid may be preferred, due to the high ozone decay rate, which significantly reduces the concentration of ozone applied to the wafer surface.
In view of these concerns, there is a need for an apparatus and method for treating a surface of a semiconductor wafer with both a desired processing fluid and ozone such that a high concentration of ozone can be applied to the wafer surface to effectively oxidize materials on the wafer surface to clean and/or grow an oxide layer on the wafer surface.